Gas analyzing apparatus



Au 13, 1940. .1. D. MORGAN :1- AL 2,211,527

GAS ANALYZING APPARATUS Filed April 16, 1937 2 Sheets-Sheet l INVENTORSJOHN D. MORGAN BALAN P. W

Patented Aug. 13, 1940 UNITED STATES ATENT orlcs GAS ANALYZING APPARATUScorporation of Maine Application April 16, 1937, Serial No. 137,168

2 Claims.

This invention relates to the analysis of gases, and more particularlyto apparatus adapted for checking the operating efficiency of domesticspace heating furnaces and Diesel engines in accordance with thetemperature and composition of gaseous products of combustion therefrom.The apparatus of the present invention is a continuation in part of andimprovement on that described in our copending applications, Serial No.688,972, filed September 11, 1933, which is now U. S. Patent No.2,073,249, granted March 9th, 1937; and Serial No. 755,692, filedDecember 3, 1934.

The primary object of the present invention is to provide improvedapparatus which shall be adapted to use in adjusting all such combustionoperations to a condition of optimum operating efficiency with respectto the particular combustion apparatus and fuel under test. A feature ofthe invention which is designed to accomplish the aforementioned objectconsists in apparatus adapted for making substantially simultaneousmeasurements of the factors of flue gas temperature and amountsof'unburned combustible and of excess air in the flue gas at severalpoints on the load curve of the furnace or engine between high and lowload. The operation of the combustion apparatus under test can then beregulated in accordance with such measurements by proportioning the fueland air supplies to the furnace or engine so that the temperature of theproducts of combustion is at a minimum point with the combustionapparatus set at normal operating conditions to meet an average load.

Domestic heating furnaces and Diesel engines normally operate best undera condition of OVBI"? ventilation wherein the products of combustionleaving the combustion chamber may contain small amounts of unburnedcombustible and relatively large amounts of excess air. a

A particular object of the present invention is to provide apparatuswhereby even an unskilled operator can obtain accurate and substantiallysimultaneous measurements of the temperature and composition of gaseousproducts of combus tion containing both relatively large amounts ofexcess air and relatively small amounts of un burned combustible.

A combustion analyzer which is calibrated for accurately measuring smallamounts (for example, under 1%) of unburned combustible in flue gas, cannot normally be used without re-calibration for measuring large amounts(100-l.50%) of excess air. This is because of the wide variations intemperatures which are developed on the one hand in burning smallamounts of unburned combustible contained in a flue gas sample, and onthe other hand in burning the large volumes of excess air which may becarried by the same flue gas; and because it is difiicult to calibrate 5millivoltmeters or light sensitive instruments to record accurately overa Wide range of temperature.

Accordingly, another object of the present invention is to provideapparatus which shall be in operative for making substantiallysimultaneous quantitative analyses of flue gases by combustion both fora very low content of unburned combustible and for a very large contentof excess oxygen or air. 15

The apparatus of the present invention has been particularly designedfor making continuous measurements of the temperature of flue gasadjacent the point at which it leaves the combustion chamber and for thesimultaneous removal of a sample stream of the flue gas at the point oftemperature measurement, division of the stream into two uniformlyproportional portions, and quantitative analyses of each portion of fluegas by combustion. The analysis of one portion 25 is efiected afteraddition thereto of a-measured uniform amount of vaporized liquid fuelfor the purpose of determining the excess air therein; while asubstantially simultaneous analysis is made of the other portion of fluegas afteracldition of air thereto to determine the amount of unburnedcombustible therein.

The invention contemplates taking such flue gas temperature measurementsand simultaneous measurements of unburned combustible and of excessoxygen in the flue gas while operating the combustion apparatus undertest to meet vary ing conditions of heat demand, followed by adjustmentof the air and fuel supplies to the combustion apparatus so as toreducethe tempera 4O ture of the outgoing flue gas to a minimum point Whileburning fuel in amount suflicient to meet a normal or average load onthe apparatus.

The invention will now be more particularly described by reference tothe accompanying drawings, which illustrate apparatus embodying apreferred form of the invention.

In the illustrated apparatus--v Fig.1 is a diagrammatic flow sheet of'the apparatus assembly, showing the gas analyzer unit and the fuelvaporizer in section and the other parts of the apparatus in elevation;

Figs; 2, 3, 4 and 5 illustrate alternative positions of the aperturedgas flow regulating valve and combined multiple electric switch, whichhave been illustrated in in the setting cmployed for measuring theamount of excess air in the flue gas under analysis;

Fig, 6 is a wiring diagram; and

Fig. 7 shows in perspective a preferred design for the multi-aperturedgas flow regulating valve and the multiple switch opcratively therewith,together with the orifice block wit n which the valve is rotatablyjournaled.

Fig. l of the drawings illustrates an application of the invention tothe regulation of combustion in a domestic type heating furnace, but itwill be readily understood that the invention is equally applicable tothe regu ion of combustion in Diesel engines and similar combustionunits.

Referring to Fig. 1, numeral iii designates a gas sampling tube havingan apertured gas sampling nozzle l2 at its inlet end, said nozzle beingadapted for introduction in the waste gas flue M of a furnace IE forsecuring a continuous sample of the furnace flue gas to be analyzed. Athermocouple i8 is mounted in flue i i closely adjacent the gas samplernozzle l2, and lead Wires 26 and 22 connect the thermocouple it to amillivoltmeter Zfl which is calibrated for measuring the temperatures ofthe flue gases in flue id at approximately the point where the flue gassample is taken.

The discharge end of sampling tube i9 is ported out through an L-fittinginto a gas filter and liquid separator 26. Filter 26 is preferablyfilled with copper filings, cotton, glass wool, and/or other dryfiltering material, and the filter design includes a bafiie 28 aroundwhich the gas passes before leaving the filter through an L-fitting andtube 30 on its way to the gas analyzing apparatus. Tube 38 communicablyconnects the interior of filter 25 with an aperture 3?; in an orificeblock 34. A multi-apertured gas flow regulating valve 36 is rotatablyjournaled in block 34 (Fig. 7). With the valve set in the position showndiagrammatically in Fig. l and in Fig. '7 for analyzing the flue gasesquantitatively for excess air, all of the sample of flue gases which isconducted to the aperture 32 in the orifice block from the filter 25flows from aperture 32 into a peripheral groove 3?. From groove 3! thegas flows through an orifice 38 in the valve 36 into another groove 39in the valve periphery and thence through another aperture 41 in block34 into a conduit through which the gas sample passes to a T-fitting 32where the gas stream is divided into two uniformly proportionalportions. From the T-fitting 52 one of the portions of flue gas passesinto the suction side of a pump 44, which is illustrated as a rotarypump (i. e., a pump with a rotary piston). Pump a l has an air inletaperture 4B communicating with its suction side, by means of which airin measured amount is sucked into the pump chamber from atmosphere alongwith the portion of flue gas and mixed within the pump prior todischarge of the flue gas air mixture through a tube 48 communicatingwith the discharge or pressure side of the pump. This air is addedto'insure suificient air to completely burn any unburned combustible inthe gas sample.

The second portion of flue gas is drawn from the T-fitting 42 into thesuction side of a second rotary piston pump 59, and after having itspressure raised by the pump is discharged into a tube 52 whichcommunicably connects with another aperture 54 in the orifice block 34.With the valve 36 set in the position illustrated in Figs. 1 and 7, theaperture 55 in the orifice block communicably connects with a groove 38in the side wall of valve St and at the same tin c groove 53communicably connects with another aperture 53 in orifice block 3- 3.Aperture $3 in turn cornmunicates with a tube whereby the sample of fluegas which has passed through. the pump 53 is conducted into the inletport of a thermostatically controlled wick vaporize: In flow ing throughthe vaporizer E2 the gas sample is carbureted by admixture therewith ofliquid fuel vapors, and from the dischar; port of the vaporizer the fluegas-fuel vapor mixture is retiuned to the valve 36 through a pipe i iand an aperture 66 in the orifice bloc. t l. With the valve 36 set inthe position ill rated in l and 7 aperture 653 communicably connectswith a groove 58 in the side wall of valve and at the same time grooveF58 communicably connects with another aperture id in orifice block 35.From aperture I i, the mixed flue gas-fuel vapor mixture passes througha tube 7? into a gas inlet chamber l4 which is located on one of gasanalyzer block 76. While the sample of which has passed through thevaporizer (Fig. 1) enters the chamber H in the analyzer, the othersample of gas which has admi e c: with air during its passage throughpump ii simultaneously enters a second chamber 78 in the analyzer fromthe tube 58.

With the valve 36 turned counter-clockwise from the position shown inFig. 1 to a new position (Fig. 5) which is used for calibrating the zeroposition of the side of the analyzer which is adapted for analyzing forexcess air, the which is handled by the pump 5:": lay-pas 'es thevaporizer 62 and is conducted through aperture 5 and valve groove 58directly to aperture it in the block 3 and thence through pipe 1'2 intoanalyzer inlet chamber M. However, with the valve set in the positionillustrated in Fig. 5, it is air rather than flue gas whic enters thechamber Hi. In other words, with the valve set in the positionillustrated in Fig. 5 the aperture 38 in the valve no longercommunicates with the flue gas supply pipe but the inlet side of thepipe 48 communicably connects through a semicircular groove ll' andradial aperture in valve 36 with a central bore 8G in a stem 92 of valve36, in which position air from atmosphere enters the bore 89 fromatmosphere at point under the suction of pumps 44 and 58.

With the valve 35 turned counter-clockwise 9Tl from the position whichis shown in Fig. 5 to a new position shown in Fig. 4 which is used forcalibrating the analyzer and for setting the v2- porizer 632 formeasuring full scale deflection of the millivoltrneter when set foranalyzing for excess air, it will be noted that air still enters thepump 50 through groove 7'! and aperture '58 in the valve and tube Q6. Inthis case, the air passes from the discharge of pump through groove 68in the valve and thence through the vaporizer where liquid fuel vapor isadmixed therewith prior to conducting the airvapor mixture back throughgroove in the valve and pipe 12 to chamber i l.

With the valve 36 turned. another 90 counter clockwise from the positionshown in Fig. 4 to a new position (Fig. 3) which is used for calibratingthe zero position of the analyzer when set for analyzing forcombustible, air still enters the tube 30 through the air entrance boreElf! and valve aperture 18 and a portion of this air is ill] passed bythe pump 44 into the analyzer chamber 16.

In Fig. 2, still another position of the valve 30 is shown with thevalve turned about counter-clockwise from the position illustrated inFig. 3. With the valve in the position illustrated in Fig. 2, theanalyzer is set for analyzing for combustible in the flue gas, and itwill be noted that the gas flow connections are the same that areoperative with the valve in the position shown in Fig. 1. In otherwords, the only difierence which is efiected by the small change in thevalve position as shown in Fig. 2 over that shown in Fig. l is in thesetting of an electrical control switch H3 which is mounted on stem 82of the valve and which will be more fully described hereinafter inconnection with the description of the electrical circuit.

The apparatus is normally calibrated by first setting the valve 35 inthe position illustrated in Fig. 3 and checking the zero position of thecombustible side of the analyzer, then checking the zero position of theexcess air side of the analyzer by turning the valve 180 in eitherdirection to the position shown in Fig. 5, and then turning the valve 90counter-clockwise to the position shown in Fig. 4 to calibrate thevaporizer. As shown in the drawings, the position of the valve when setfor obtaining a reading of the amount of combustible (Fig. 2) is 30counterclockwise from the position of the valve (Fig. 1) when set for areading on the amount of excess air in the gas under analysis. Thegroove l? in the periphery of the valve is out long enough to registerwith aperture ll during 180 of valve throw.-

Grooves 5t and 58 are each out long enough to register with one ofapertures 50, 58, 00 and H0 over 105 of valve throw; and grooves 3'! and39 are out long enough to register with apertures 32 J l and llrespectively over 30 of valve throw.

The vaporizer 02 is mounted over a liquid fuel reservoir M from whichliquid is elevated into the vaporizer by a wick 86 which extends upcentrally through the vaporizer. An electric resist- .I- ance heatingcoil lit is mounted integrally with that portion of the wick whichextendsinto the vaporizer, and the wick is supported within thevaporizer by a bi-metallic strip 90 which is pivotally supportedcoaxially of the vaporizer and coil 35 by an apertured plug closure 92at the base of the vaporizer between the vaporizer and the reservoir M.It will be understood that the lower end of the wick dips into theliquid fuel in reseri ground d terminal post 0% to which the pivotedend. of strip 90 is connected.

The temperature which is maintained in vaporizer 52 controls the amountof fuel vapor which is admixed with the portion of flue gas flowing intothe analyzer chamber M with the valve 35 set in the positionsillustrated in Figs. 1, 2, and 4:. The spring strip 00 is supported sothat its free contact end Hit tends to hold contact with bimetallicstrip 00 at temperatures above the maximum temperature at which it isdesired to operate vaporizer 62, while bi-metallic strip 90 iscalibrated so that its free contact end 102 tends to warp to the rightaway from the contact end I00 of strip 96 when the temperature developedby the vaporizer heating circuit exceeds a predetermined amount. Anadjustment screw Hi l is provided with an insulated end whereby the freeend of strip 00 is prevented from moving in the direction of warp ofstrip 00 when the vaporizer temperature exceeds that at which the switchis designed to break circuit.

The gas analyzer unit is supported on an orifice block H38 and embodiesa pair of spaced tubular combustion cells 508 and H0. The cells areembodied in a unitary housing comprising a block of dielectric heatinsulating material such as Bakelite. Centrally apertured dielectricplugs H2 form quickly detachable bottom closures for each of the cellsHi8 and I Hi and extend upwardly into the respective cells, and each ofthese plugs turn carries metal conductor catalyst supporting rods i itwhich also form the connecting leads for catalytic heating wires i itand H6 which are mounted respectively in the cells H18 and I ill in thepath of gas and air flowing therethrough. The cell I08 is adapted tofunction as an excess air analyzer, and as illustrated in Fig. 6, thecatalyst wire lid forms one leg of a Wheatstone bridge of which anothernon-catalyst leg is designated by the numeral H8. Legs H4 and H8 aremounted in vertical parallel relation within the cell I00. The other twolegs of the bridge are designated in Fig. 6 by the numerals I20 and 22.Since the cell I00 is designed to measure amounts of air up to 150%excess in the products of combustion under analysis, it is essentialthat the catalyst H 3 be relatively insensitive as compared with thecatalyst H5 which is employed in the combustible analyzer l lil.Experience has shown that the catalyst H0 should consist of a wire ofplatinum-iridium (5%) alloy inch in length by .005" diameter, while thewire H8 should have the same composition, diameter and length as thewire lit and should be covered with a thin gold plating to render itnon-catalytic. Gold plating is chosen for wire M3 because it will standup at operating temperatures below 1400 F., and its use insures ease ofbalancing of the conductivity of the wires H8 and lid when operating inair.

The catalyst wire M6 in the cell M0 must be many times as sensitive asthe catalyst wire H4 in cell 1108 in order to measure quantitativelysmall amounts (02-03%) of combustible in the flue gases under analysis,and accordingly this wire is constructed of substantially pure platinumhaving a length of about 1 and diameter of about .0035". As shown inFig, 6, wire H6 forms one leg of a second Wheatstone bridge circuit,said second Wheatstone bridge also embodying a non-catalyst leg arewhich is likewise mounted within the cell M0, the other two legs ofthebridge being indicated in Fig. 6 by the numerical designations E25and 628. The non-catalytic leg I24 is preferably constructed of platinumrhodium (5%) alloy wire of the same length as catalyst M6 and having adiameter of about .003", plated with a nickel oxide coating of about000% inch thickness. Nickel oxide is employed for coating the wire 12sin the cell M0 for the reason that this cell is designed to developtemperatures of about; 1500 F., at which temperature nickel oxide ispreferred as a coating over gold. The nickel oxide coated wire i2 5 hasa darker color and more heat radiating capacity but a smaller diameterthan the opposite platinum cat-' alyst leg of the bridge in order tocounterbalance the effect that wires coated with nickel oxide operate ata lower temperature in air than bare platinum wire when in air, and at ahigher temperature than platinum when in an atmosphere containing CO2,at the normal operating temperature range of the catalyst. As shown inFig. 1 the supporting metal posts for the catalyst and non-catalyticlegs of the respective bridges which are mounted within the cells I88and III) form the conjugate connections for the bridge through terminalposts Hill-I32, I38I58.

The central apertures in each of the plug closures H2 at the lower endof each of the cells I88 and I I communicate at their lower ends withthe respective gas supply chambers 18 and 16, and at their upper endscommunicate through radial apertures 34 with the interiors of therespective combustion chambers. Also each of the catalytic wires in therespective chambers is enclosed within a cylindrical shield I 85 whichis open at the top. The shield I36 in the combustible analyzer cell I18also has an aperture I88 therein about opposite the lower end of thecatalyst through which gas flowing around the shield can diflfuse andpass through the shield into contact with the lower end of the catalyst.A bimetallic strip thermostat I48 is hung on the outside wall of theshield I88 in cell H8 in position to control the opening and closing ofthe aperture I 38 in accordance with the temperature which is developedwithin the cell l8.

Openings I42 and Hi l are provided in the analyzer block 16 at the topof each of the cells I08 and I I8 respectively by which unburned gasesand products of combustion may escape from the analyzer cells toatmosphere.

The rotors of pumps 44 and 59 are mounted on the drive shaft of a smallconstant speed electric motor I46 which is powered. by current flowingthrough an electric circuit I48 and controlled by a panel mounted switchI58. The main circuit leads from the switch IE8 are connected across thebrushes of the motor I48, and from these same leads the electrical poweris taken for heating the catalyst wires IM and MB of the Wheatstonebridges. The voltage of the current used for heating the catalystelements of the bridges is reduced by means of a transformer i152 to anapproximate value of 5 to 6 volts. To accomplish this, the A. C. currentfrom the main supply circuit I l8 flows through a ballast or constantcurrent glow lamp I54 to the high voltage side of the transformer M2,and from the low voltage side of the transformer the current flows theprimary side of a full wave rectifier $55 which is in the form of abridge (Fig. 6), The rectified D. C. current of about 1.75 amperes, istaken from secondary points on the rectifier which are connected topoints I58 and I88 of the respective Wheatstone bridges. The currentflowing through the secondary circuit of the transformer E52 passesthrough a variable resistance or rheostat I62, and the current flowingthrough each of the Wheatstone bridges is controlled by zero adjusterrheostats I64 and I68 which are connected in shunt circuit respectivelyacross the catalyst legs H6 and H4. The fixed resistances E26, I28, I28and I22 are preferably mounted on spools secured within the analyzerblock and may be balanced as to dimensions and composition with thecorresponding legs H6, I28, IM, and H8 The rheostats I64 and I66 areemployed for adjusting the current supplies to each of the bridgesembodying the catalyst wires II 6 and H4, respectively.

A millivoltmeter I68 is provided for the purpose of measuring anydifferential current flow developed in the Wheatstone bridges as betweenthe catalyst and the non-catalytic legs. The millivoltmeter I68 isprovided with two scales, one of which is calibrated to measurepercentages of excess air present in the gas stream flowing through thecell I88, while the other scale is designed to measure small percentagesof combustible in the gas stream flowing through the cell I II]. Thevoltmeter is connected alternatively either to points I18 and I12 of theWheatstone bridge having its active and inactive legs mounted in thecell I88, or to points I14 and I16 of the Wheatstone bridge having itsactive and inactive legs mounted in the combustion cell H0. Thisalternative connection of the voltmeter to either one or the other ofthe two Wheatstone bridges is effected through a doublepole-double throwswitch I18 which is illustrated diagrammatically in Fig. 6, and apreferred mechanical design of which is illustrated in Fig. 7. As shownin Fig. '7, the essential parts of the switch I18 comprise 6 disks I 88of insulating material rotatably journaled on stem 82 of valve 36, eachdisk I88 having a split metal conductor ring mounted thereon, and eachdisk contacting at its periphery a spring contact member I82.

The rheostat I66 is provided for the purpose of balancing the Wheatstonebridge having its active leg in cell I88. The rheostat I64 provides asimilar adjustment for the bridge embodying catalyst H6.

Current for heating the coil 88 of the vaporizer 62 is taken from asecond transformer I83 in the main circuit.

In the ordinary operation of the apparatus a dial I88 which is journaledon the front or panel end of valve stem 82 may be first turned to movethe valve 36 to the position shown in Fig, 5 for the purpose ofcalibrating the excess air side of the analyzer on air admitted to theapparatus through the bore 80 in the valve stem. The dial I88 may nextbe turned to the position illustrated in Fig, 4 in order to permitcalibrating and adjustment of the excess air analyzer and of thevaporizer so that the indicator pointer of the millivoltmeter I68 willremain on the millivolt scale at about the maximum swing from the zeroposition of the scale when vaporizing sufiicient liquid to give a fullscale deflection of the voltmeter when the same amount of liquid isvaporized in a gas containing approximately 150% of excess air. The dialI88 is next turned to the position shown in Fig. 3 for the purpose ofcalibrating the combustible side or the analyzer on air. The dial maythen be turned to either of the positions shown in Fig. l or 2,depending upon whether measurements are to be taken of the amount ofexcess air in the flue gas, or the amount of unburned combustible in theflue gas. The analyzer when properly calibrated is adapted for taking asubstantially simultaneous reading of excess air and combustible, sinceboth cells I88 and III] are operating continuously and all that isnecessary to take a reading of the operation in one cell or the other isto connect the voltmeter I68 with the Wheatstone bridge in which theactive catalyst leg in the cell under examination is embodied.

After calibrating both sides of the analyzer the sampling tube I2 isplaced in the flue of the furnace, and with the valve 36 and switch I18in position for analyzing for excess air (Fig. l with the vaporizer 62in the gas circuit to analyzer chamber I08), a continuous sample of theflue gas is drawn at a substantially uniform rate through the filter 26into T-fitting 42, from which one portion of the sample flows throughpump 553 into vaporizer E2, and. a continuous sample of the gas admixedwith vaporized fuel flows from the vaporizer through analyzer cell I08.Simultaneously another portion of the gas sample is conducted fromT-fitting 62 through pump M where it is admixed with air, and from pump4d a continuous sample of the gas admixed with air passes into andthrough analyzer cell I II).

The gas samples enter both analyzers I08 and I I0 under a constantpressure and at a constant rate. All of the excess air in the gas sampleentering analyzer which the gas exhausts through passage 9 Similarly,all of the unburned combustible in the gas-air mixture entering analyzerH0 is burned therein before the gas is exhausted to atmosphere. Thecatalytic combustion which occurs in the analyzer cells I08 and H6increases the temperatures of the respective catalyst wires II4 and H6,thereby reducing the current flow through said wires and upsetting thebalance of the respective bridges in which said catalyst wires areembodied. With the switch I'I8 connecting the voltmeter I63 in circuitwith the VVheatstone bridge embodying catalyst II I as a leg, theincreased temperature which is developed on the catalyst wire H4 ismeasured on the excess air scale of the millivoltmeter in terms ofpercentage excess air in the flue gases. With the switch Ht thrown inthe opposite position to incorporate voltmeter I58 in circuit with theWheatstone bridge embodying catalyst wire H6 as a leg, the increasedtemperature which is developed on the catalyst I I6 is measured on thecombustible scale of the voltmeter in terms of percentage combustible inthe flue gases.

Prior experience has shown that great care must be taken in choosing thetype of fuel which is added to a sample of flue gas for the purpose ofburning out any excess air in a combustion analyzer. Hydrocarbon fuelsare unsatisfactory for this purpose because they develop such hightemperatures on combustion that cracking reactions generally occur, withresultant erroneous readings for excess air by reason of incompletecombustion reactions and waste of part of the heat developed inpromoting secondary and endothermic reactions. Gases such as hydrogenare also unsatisfactory for analyzing flue gas for excess air,apparently as a result of the fact that hydrogen occludes in the poresof metal parts of the analyzer and of the catalyst. Oxidizedhydrooarbons of low calorific value such as meth- IlJB is burnedtherein, after anol can be used satisfactorily for analyzing amounts ofexcess air in the flue gas within the range normally contemplated in thepractise of the present invention, provided that the supply of vaporizedmethanol is regulated so asto effect complete combustion of the airwhile developing temperatures in the catalyst within the measuring rangeof the analyzer. Other oxidized hydrocarbons may be employed in place ofmethanol provided that their calorific value lies in the range of from5600 to 7600 gram calories per gram. For example, acetone and ethylacetate and mixtures of methanol and ethyl acetate have been found to besatisfactory fuels adapted for use in the vaporizer 62. With fuels ofthe type indicated the operating temperature of the vaporizer normallylies in the range F.- F. when flowing therethrough unheated flue gas ata rate of 50-100 cu. in. per minute over an exposed wick surface notsubstantially exceeding 1 sq. in. in area.

The invention having been. thus described, What is claimed as new is:

i. In a gas analyzer having a combustion cell, a Wheatstone bridgeelectric circuit embodying a catalyst wire leg and a non-catalyst wireleg mounted in said cell in parallel vertical position, means fordelivering gas to be analyzed at a controlled rate to said cell, thecombination with said combustion cell of means for directing the gasover the catalyst and non-catalyst legs at a uniform rate comprising acylindrical shield disposed around the catalyst and non-catalyst legsapertured in a plane adjacent the upper end of each leg for affordinguniform access of gas to both legs, there being a lower aperture in saidshield in approximately the plane of the lower portion of the legs,together with a bimetallic strip thermostat valve for controlling theopening and closing of said aperture in accordance with the temperatureobtaining in the combustion cell.

2. In a gas analyzer, a vertically disposed combustion chamber, meansfor passing a continuous stream of gas to be analyzed at a controlledrate upwardly through the chamber, a cup-shaped shield mounted centrallywithin the chamber with its base and side Walls positioned in bafflingrelation to the stream of gas flowing upwardly therethrough, said shieldbeing provided with an aperture adapted to afford access of gas to theinterior thereof, a Wheatstone bridge electric circuit embodying acatalyst wire leg and a noncatalyst wire leg of approximately balancedelectrical conductivity mounted in closely spaced parallel relationwithin said cup, and a valve member mounted in operative position tovary the flow of gas through said shield aperture.

JOHN D. MORGAN. ALAN P. SULLIVAN.

